This invention relates to decorative transfer of images to various types of coarse surfaces.
Hot stamping of metallic foils has been widely used for decorating, with graphics and text, such items as book covers, wallets, attache cases, handbags, and suitcases. These articles are made of leathers, vinyls or textiles, which have surfaces with deep grains or fibers having valleys, for example, 0.001 inches or even 0.003 inches in depth. For decorating purposes, the metallic foil, transferred by heat and high pressure, typically has a mirror-like surface for shiny appearance. Furthermore, the transferred material includes a tinted or clear lacquer top layer covering the metal surface to provide protection and a rich gold or other appearance. Traditionally, to transfer the metallic material, one has to first fabricate a custom- made metal die with raised and recessed areas corresponding to the particular design. The raised areas press the foil against the receiving substrate to transfer the material having the desired pattern while heat is applied. The stamping press applies pressures of hundreds of pounds or more to the die. While this type of transfer has been widely used, it also has drawbacks. For example, it takes a relatively long time to fabricate the die and the fabrication process is relatively expensive.
There are other widely used techniques for decorative printing, but they also require fabrication of special tools for different designs. For example, silk screen printing requires fabrication of a print screen and pad printing requires fabrication of a pad.
Computer controlled thermal printing is a different thermal process. It uses a thermal printhead controlled by a computer to print an image, typically, on paper. The thermal printhead generates heat localized over dots of a computer generated pattern to be printed. A thermal printing ribbon, disposed between the printhead and the paper or other web, releases ink that is thermally transferred in tiny amounts to the paper. The ink layer consists of a particulate or liquid-like material. The thermal printing ribbon also includes constituents that facilitate good adherence of the ink dots to the paper surface. The entire process is relatively fast and economical. However, this process has not been equated with hot stamping because of limitations of the process and the materials on which a precise image can be formed.
Thermal printing has been used for decorative printing on papers of varying surface qualities. To improve the quality of the transferred image, printheads have been used to transfer several layers of ink on the same dot or puffing particles have been included in the transfer composition to fill irregularities on the printed surface. In either case, the thermal printing process and its effects have differed significantly from the hot stamping process that transfers relatively larger chunks of metallic material to the surface to achieve a specular effect.